[1.21.3] Append unknown modded flags to removed_features level data

[ApexModder]

In vanilla Mojang has data fixers which appends all legacy/removed feature flags to a list (removed_features) in the level data, allowing crash reports to be aware of which flags were active and have since been removed.

This PR implements a simple hook to append unknown modded flags to this list, allowing modders to know if a crash happened in an environment where their alpha testing was once enabled.

An example crash report can be found here, take note of the Removed feature flags: entry, which lists all our test flags.

[neoforged-pr-publishing]

• Publish PR to GitHub Packages

Last commit published: 3bb85857dddd441356f4b453557f84c54f76dc04.

PR Publishing

The artifacts published by this PR:

• 📦 net.neoforged:testframework:21.3.42-beta-pr-1703-pr-removed-flags
• 📦 net.neoforged:neoforge:21.3.42-beta-pr-1703-pr-removed-flags

Repository Declaration

In order to use the artifacts published by the PR, add the following repository to your buildscript:

repositories {
    maven {
        name 'Maven for PR #1703' // https://github.com/neoforged/NeoForge/pull/1703
        url 'https://prmaven.neoforged.net/NeoForge/pr1703'
        content {
            includeModule('net.neoforged', 'testframework')
            includeModule('net.neoforged', 'neoforge')
        }
    }
}

MDK installation

In order to setup a MDK using the latest PR version, run the following commands in a terminal.
The script works on both *nix and Windows as long as you have the JDK bin folder on the path.
The script will clone the MDK in a folder named NeoForge-pr1703.
On Powershell you will need to remove the -L flag from the curl invocation.

mkdir NeoForge-pr1703
cd NeoForge-pr1703
curl -L https://prmaven.neoforged.net/NeoForge/pr1703/net/neoforged/neoforge/21.3.42-beta-pr-1703-pr-removed-flags/mdk-pr1703.zip -o mdk.zip
jar xf mdk.zip
rm mdk.zip || del mdk.zip

To test a production environment, you can download the installer from here.